The present disclosure relates to a light-emitting element and a method for production thereof More particularly, the present disclosure relates to an organic electroluminescence element and a method for production thereof
The organic electroluminescence display device, which employs the organic electroluminescence element, has recently been attracting keen attention on account of its potential for replacing liquid crystal display devices. (Electroluminescence will occasionally be abbreviated as “EL” hereinafter.) The organic EL display device is of self-luminous type and is characterized by low power consumption. Moreover, it is expected to rapidly respond to high-speed video signals for high-definition display. Therefore, great efforts are being directed to its development and commercialization.
An organic EL element is usually composed of a first electrode, an organic layer (which has a light-emitting layer made of organic light-emitting material), and a second electrode, which are sequentially arranged in a laminate structure. Attempts are being made to incorporate the organic EL element with a resonator structure or to optimize the thickness of each layer as a constituent of the organic layers, thereby controlling the light that is generated in the light-emitting layer, in anticipation of improvement in color purity (of emitting light) and light emitting efficiency. (See PCT Patent Publication No. WO01/39554 pamphlet (hereinafter referred to as Patent Document 1), for instance.)
It is desirable to keep resonance as weak as possible or to keep the organic layer as thin as possible because the intensity of resonance or the thickness of the organic layer makes chromaticity and brightness much dependent on the viewing angle. In other words, the increased viewing angle results in a considerable shift of the peak wavelength in the spectrum of light emitted from the organic EL display device or a great decrease in the intensity of light. (See Patent Document 1.) However, the disadvantage of making the organic layer thinner is that the organic layer is not covered completely if there exist particles (foreign matter) and projections on the first electrode, as schematically shown in FIG. 18, and this incomplete covering would result in short circuits between the first electrode and the second electrode. In the case of organic EL display device of active matrix type, such short circuits result in missing pixels to aggravate its display quality. In the case of organic EL display device of passive matrix type, too, such short circuits result in missing lines. Such missing pixels or lines are a serious problem particular in the case of large-sized organic EL display device, which requires vigorous viewing angle characteristics and low tolerances for defects per unit area.
So far, many attempts have been made to reduce short circuits between the first electrode and the second electrode. For example, Japanese Patent Laid-open No. 2002-035667 (hereinafter referred to as Patent Document 2) discloses an organic EL display device of bottom emission type in which a high-resistance layer is inserted between the anode electrode and the organic film. Japanese Patent Laid-open No. 2006-338916 (hereinafter referred to as Patent Document 3) discloses an organic EL display device of top emission type in which the anode electrode is doubled and the anode electrode close to the organic layer is a high-resistance layer. Japanese Patent Laid-open No. 2005-209647 (hereinafter referred to as Patent Document 4) discloses an organic EL display device of bottom emission type in which the cathode electrode is doubled and the anode electrode close to the organic layer is a high-resistance layer.